The present invention relates to rotary actuators with clutching and declutch mechanisms that enable the output member to be rotated by a hand wheel whenever operation of the drive motor temporarily ceases.
The primary drive mechanism for the rotary actuator is an electrical drive motor. During utilization of the actuator, however, a secondary drive mechanism must be provided in case of the occurrence of a power failure, failure of the motor, or the need of manual adjustment. Often during the initial start-up of the valve that is being operated by the rotary actuator, it is desirable to be able to operate the actuator manually before placing the motor into operation. In order to accomplish all of these purposes, a secondary source of power, a hand wheel is provided for manually rotating the actuator.
A clutch mechanism and a declutch mechanism are provided for switching the rotary control of the actuator between the drive motor and the hand wheel. While both rotary actuators per se and clutching and declutch mechanisms incorporated in such actuators are well known in the art, the various devices that have been provided are relatively complex which increases both the cost of manufacturing and maintenence of such equipment.
Exemplary of the current state of the art of rotary actuators with declutch mechanisms in U.S. Pat. No. 4,022,309 to Denkowski et al. The valve operating mechanism disclosed by this patent includes both motor and manual drive devices for driving an externally threaded drive stem. The driving force is applied through a worm shaft and a worm to a worm gear. The worm gear has upstanding lugs that engage a pair of lugs that extend downwardly from a motor clutch ring. The clutch ring through a pair of detent rollers arranged within a plurality of corresponding slots drives a cup shaped drive ring that is positioned in the motor clutch ring. The lower portion of the drive ring is connected through splines to the drive sleeve. The drive sleeve in turn is internally threaded so as to be engaged with the externally threaded valve stem. When the motor power is either intentionally deactivated or a failure has occurred, the actuator mechanism can be declutched so as to switch between the motor mode of operation and a manual mode of operation. A crank or a lever can be manually rotated so as to turn a pinion declutch shaft. Secured to the declutch shaft is a pinion that has a fixed number of teeth arranged in engagement with circumferential grooves on a clutch sleeve. Arranged below the clutch sleeve is a lug ring. That lug ring is supported in an annular floor of a drive ring. The lug ring has a pair of opposing slots that are located to receive downwardly extending legs of the clutch sleeve. A pair of opposing lugs, which are spaced 180.degree. apart, extend radially outwardly from the wall of the lug ring. Lugs are located in the upper half of the lug ring wall. In the lower part of the lug ring wall are a pair of recesses which serve to receive the detent rollers.
Numerous other patents disclose various embodiments of rotary actuators many of which have clutch and declutch mechanisms for alternatively coupling the output member to an electrical motor or a hand wheel. Exemplary of such actuators are those illustrated in the following U.S. Pat. Nos. 2,694,320 to Kron; 3,168,841 to Caldwell et al.; 3,198,033 to Fry; 3,257,866 to Fry; 3,279,376 to Fry; 3,298,249 to Nott; 3,585,867 to Grimshaw et al.; and 3,603,175 to Horton. In addition to the complexity of the clutch and declutch mechanism included within these patents, the layout of the systems renders it extremely difficult to replace the stem nut to which the threaded driving rod of the actuator is attached.
During utilization of the actuator, depending on the nature of the member to be controlled, various sized driving rods are employed. Within certain limits, the same actuator can be used with different sized threaded driving rods. In order to accomodate the different sized rods, the stem nut within the actuator that is rotated and transmits the rotary force to the driving rod can be changed. With the various actuators disclosed in the above-noted list of patents, however, in order to change the stem nut, the rotary actuator must be detached from the valve being controlled. In these actuators, access to the stem nut can only be obtained from the output side of the actuator.
For example, in the embodiments disclosed in U.S. Pat. No. 3,279,276 to Fry, the nut member is attached in such a manner so as to require the actuator to be removed in order to remove the nut member. More specifically, it is indicated that the nut member is arranged so as to abut the end surface of the output shaft. The output shaft has a sleeve with a flange thereon that engages beneath the flange of the nut member so as to maintain the nut member in engagement with the output shaft. Consequently in order to remove the nut member it is necessary to remove the actuator assembly so that the flange on the output shaft can be removed.
As another example, in U.S. Pat. No. 3,585,867 to Grimshaw et al. it is indicated that the driving engagement mechanism is engaged in a recess at the driving end of the output shaft. An output member is connected to the driving engagement mechanism so as to extend along the output shaft in one or the other direction. Since the driving engagement member is arranged within the recess at the bottom of the shaft, it is necessary to remove the entire shaft which is secured within the actuator in order to be able to remove the driving engagement mechanism, more particularly, the stem nut.